Immunoglobulin (Ig) light chain restriction (LCR) detection is an important molecular diagnostic tool in the differential diagnosis that includes lymphoid hyperplasia, atypical lymphoid hyperplasia, chronic inflammation, and B cell neoplasms. Current methods of LCR identification in formalin fixed paraffin embedded (FFPE) tissue include immunohistochemistry (IHC) and conventional chromogenic in situ hybridization (CISH), which measure kappa or lambda protein and mRNA, respectively. However, both IHC and conventional CISH lack sufficient sensitivity to detect LCR in many non-Hodgkin lymphoma (NHL), including the most common NHL variants - follicular lymphoma, diffuse large B cell lymphoma, small B lymphocytic lymphoma, and extranodal marginal zone lymphoma of MALT type. RNAscope is novel RNA in situ hybridization technology that has single-molecule detection sensitivity and is fully compatible with FFPE tissue using either chromogenic or fluorescent detection. We hypothesize that RNAscope will accurately and reproducibly delineate LCR in all non-Hodgkin lymphoma types. We propose to develop an RNAscope-based CISH assay for kappa and lambda mRNAs for LCR detection in FFPE tissue. PUBLIC HEALTH RELEVANCE: The diagnosis of lymphoma can be difficult based on morphology alone. Detection of restricted immunoglobulin light chain expression is a molecular ancillary tool to resolve ambiguous lymphoproliferative disorders. The proposed product based on RNAscope will provide superior sensitivity to current methods.